Dog Tails - Why Dogs Wag Their Tails

(Excerpt from How to Speak Dog) Dr. Stanley Coren

“….In some ways, tail-wagging serves the same functions as our human
smile, polite greeting, or nod of recognition. Smiles are social
signals, and human beings seem to reserve most of their smiles for
social situations, where somebody is around to see them. Sometimes,
vicarious social situations, as when watching television or
occasionally when thinking about somebody special, can trigger a
smile. For dogs, the tail wag seems to have the same properties. A
dog will wag its tail for a person or another dog. It may wag its
tail for a cat, horse, mouse, or perhaps even a butterfly. But when
the dog is by itself, it will not wag its tail to any lifeless
thing. If you put a bowl of food down, the dog will wag its tail to
express its gratitude to you. In contrast, when the dog walks into a
room and finds its bowl full, it will approach and eat the food just
as happily, but with no tail-wagging other than perhaps a slight
excitement tremor. This is one indication that tail-wagging is meant
as communication or language. In the same way that we don’t talk to
walls, dogs don’t wag their tails to things that are not apparently
alive and socially responsive.

A dog’s tail speaks volumes about his mental state, his social
position, and his intentions. How the tail came to be a
communication device is an interesting story.

The dog’s tail was originally designed to assist the dog in its
balance. When a dog is running and has to turn quickly, it throws
the front part of its body in the direction it wants to go. Its back
then bends, but its forward velocity is such that the hindquarters
will tend to continue in the original direction. Left unchecked,
this movement might result in the dog’s rear swinging widely, which
could greatly slow its rate of movement or even cause the dog to
topple over as it tries to make a high-speed turn. The dog’s tail
helps to prevent this. Throwing the tail in the same direction that
the body is turning serves as a sort of counterweight, which reduces
the tendency to spin off course. Dogs will also use their tails when
walking along narrow surfaces. By deliberately swinging the tail to
one side or the other in the direction opposite to any tilt in the
body, the dog helps maintain its balance, much the same way a circus
tightrope walker uses a balance bar. Quite obviously, then, the tail
has important uses associated with specific movements. However, the
tail is not particularly important on flat surfaces, when a dog is
simply standing around or walking at normal speeds. At these times,
it becomes available for other uses. Evolution again seized an
opportunity and now adapted the tail for communication purposes.

It is something of a surprise to many people to learn that puppies
don’t wag their tails when they are very young. The youngest puppy I
ever saw systematically wagging its tail was eighteen days old, and
both the breeder and I agreed that this was quite unusual. Although
there are some differences among the various breeds, the scientific
data suggests that, on average, by thirty days of age, about half of
all puppies are tail wagging, and the behavior is usually fully
established by around forty nine days of age.

Why does it take so long for the puppy to start wagging its tail?
The answer comes from the fact that puppies begin wagging their
tails when it is necessary for purposes of social communication.
Until they are about three weeks of age, puppies mostly eat and
sleep. They are not interacting significantly with their littermates
other than curling up together to keep warm as they sleep or
crowding together to nurse. They are physically capable of wagging
their tails at this time, but they don’t.

By the age of six or seven weeks (when we start to see tail-wagging
behaviors on a regular basis), the puppies are socially interacting
with one another. Most of the social interactions in puppies consist
of what psychologists call “play behaviors.” It is through playing
that puppies learn about their own abilities, how they can interact
with their environment, and most important, how to get along with
other individuals. A puppy learns that if it bites a littermate, it
is apt to be bitten back, and perhaps the game it was playing might
be terminated by its now angry playmate. It is at this point that
the puppy also starts to learn dog language. It is not clear to what
degree these emerging social communications are prewired, but
learning is clearly needed to refine the use and interpretation of
these signals. The pups learn to connect their own signals and the
signals provided by their mother and their siblings with the
behaviors that come next. They also begin to learn that they can use
signals to indicate their intentions and to circumvent any
conflicts. This is where and when the tail-wagging behavior begins.

One place where conflicts are likely to occur is during feeding.
When a puppy wants to suckle its mother, it must come very close to
its littermates as it crowds in to find her teats. Remember that
this puppy is now coming close to the very same individuals that
might have been nipping, jostling, or chasing him a few minutes
earlier. To indicate that this is a peaceful situation, and to calm
any fearful or aggressive response by the other puppies when they
too are pushing toward the mother’s teat, the puppy begins to wag
its tail. Tail-wagging in the puppy then serves as a truce flag to
its littermates. Later on, puppies will begin to wag their tails
when they are begging food from the adult animals in their pack or
family. The puppies come close, to lick the face of the adult, and
they signal their peaceful intentions by tail-wagging. It thus
becomes clear that the reason that very young puppies don’t wag
their tails is that they don’t yet need to send appeasement signals
to other dogs. When communication between dogs is needed, they
rapidly learn the appropriate tail signals.

Tail language actually has three different channels of information:
position, shape, and movement. Movement is a very important aspect
of the signal, since dog’s eyes are much more sensitive to movement
than they are to details or colors. This makes a waving or wagging
tail very visible to other dogs.

Evolution has used a few additional tricks to make the tails even
more visible. Wild canines, like wolves, often have great bushy
tails, which are easily seen at a distance. In addition, many tails
are specially colored to facilitate recognition of tail signals.
Often, the underside of the tail is lighter, to make the high-tailed
signals quite visibly different from signals involving the tucking
of tails into a lower position. Many canines will also have
distinctive markings to make the tail tip more visible. Usually,
there is a lightening toward the tail tip, or perhaps simply a white
mark which defines the tip of the tail. In other canines, the tail
tip is noticeably darker. Either of these two color contrasts helps
to make the end of the tail more visible, and this make movement and
position cues easier to recognize….”